This invention concerns the control of annulus fluid flows in subsea oil or gas wells, and gate valves for this and other uses.
Tubing hangers for use with conventional (i.e. non-horizontal) subsea Christmas trees are known which have an annulus passage for providing fluid communication between the tubing annulus and the tree. Current methods of controlling annulus flow in this passage include:
(a) setting or removing wireline plugs in the passage;
(b) use of an annular sliding sleeve that is arranged to block or allow fluid access to the passage;
(c) a wireline actuated shuttle valve provided in the passage;
(d) an hydraulically actuated shuttle valve provided in the passage;
(e) hydraulically or electrically operated ball valves provided in the passage.
Methods (a) and (c) require wireline access to the passage. Due to reliability problems with the remote actuators concerned, it has been common to additionally provide secondary wireline actuation capability in at least method (d). Wireline valve actuation or plug is itself time consuming and unreliable, especially at increased water depths. Moreover, providing the required wireline access means that the tubing hanger annulus passage and the corresponding annulus conduit in the tree cannot be unduly convoluted or offset from the wellhead center line. These design constraints will generally enlarge the tubing hanger and tree needed for a given production bore diameter. As maximum tree weight is limited by the supply vessel crane capacity, providing tubing hanger annulus passage wireline accessibility will reduce the maximum possible production bore diameter.
An alternative approach to the control of tubing annulus fluid flows is to provide a flow loop bypassing the tubing hanger and containing suitable flow control valves. This method is used in horizontal trees as well as some conventional completion designs, for example some tubing head completions.
British Patent Reference GB 2287263 (FMC) concerns a tubing hanger having an annulus bore closeable by a rotatable disc disposed horizontally so as to intersect with the production bore.
European Patent Reference EP 0624711 (Cooper Cameron) discloses a tubing hanger having a central bore opened and closed by a gate valve. Opposed valve actuators are located on the outside of a wellhead into which the tubing hanger is run. Actuating stems extending from the actuators push the valve gate between the open and closed positions.
There is thus a need for a remotely operable, high integrity tubing annulus isolation seal system, capable of selectively sealing or providing fluid communication with the tubing annulus, preferably without the need for wirelines. It would be of further advantage if this isolation seal system could be applied to either conventional or horizontal trees, providing greater standardization design between tree types.
Accordingly the invention provides a tubing hanger having a flow passage for well fluids; a cavity contained within the tubing hanger and intersecting with the flow passage; a valve gate linearly movably received in the cavity and containing a through bore, and an actuator substantially wholly contained in the cavity arranged to move the valve gate between a position in which the through bore is aligned with the flow passage to permit fluid flow through the flow passage and through bore, and a position in which the through bore and flow passage are out of alignment so that the valve gate seals the flow passage.
Thus, the flow passage (preferably a tubing annulus passage) in the tubing hanger is effectively furnished with a gate valve, which is the preferred oil industry flow control valve, having a proven record of high sealing integrity and long term reliability. The valve gate also provides shearing capability for wirelines, coiled tubing or other objects that may be lowered through the flow passage. The tubing hanger may be for use in a conventional wellhead in conjunction with a conventional tree, or for use in a horizontal tree.
Preferably the actuator has a piston received within the cavity so as to define, in conjunction with the cavity, an enclosed space to which hydraulic fluid may be supplied to move the piston. Apart from any necessary hydraulic service line penetrations, the tubing hanger and its integral gate valve and valve actuator will thus be entirely independent of the wellhead housing; readily installable in or retrievable from the wellhead housing as a self-contained unit.
The actuator may comprise a plug which closes an outer end of the cavity. The piston may be coupled to the valve gate, for example by a pin and slot connection, allowing limited float in the valve gate in the direction of the tubing annulus passage axis. A pair of such pistons may be provided, opposed and substantially identical, with one at each end of the gate, to define a pressure balanced, double acting actuator system. One or both parts of the flow passage on either side of the valve gate may be provided with a seat pocket containing a floating valve seat for sealing co-operation with the adjacent face of the valve gate. The valve gate is preferably resiliently biased to provide fail safe closure.
Further preferred features are described below in connection with illustrative embodiments of the invention shown in the drawings.